The present invention relates generally to the field of internal combustion engines, and more specifically to engines operated under spark ignition and homogenous charge compression ignition principles.
It has been known for many years to use spark ignition, or combustion ignition concepts in internal combustion engines. In the spark ignition design, a mixture of fuel and air is provided in a combustion cylinder and compressed. A spark plug initiates combustion through the creation of an open spark sufficient to ignite the air and fuel mixture in the cylinder. Both two and four stroke operating sequences are known.
In a direct injection combustion ignition engine, such as a diesel engine, it is common to use a two stroke operating sequence. On the downward stroke of a piston in a combustion cylinder, ports for air intake are opened and a charge of air is received in the combustion cylinder. Turbochargers are often used to supply the charge air at higher pressure and density than existing ambient conditions. On the upward stroke of the cylinder, the air intake ports are closed and the air is highly compressed. At the desired point of compression, fuel is sprayed into the cylinder by a fuel injector. The fuel ignites immediately, as a result of the heat and pressure inside the cylinder. The pressure created by the combustion of the fuel drives the piston downward in the power stroke of the engine. As the piston nears the bottom of its stroke, all of the exhaust valves open. Exhaust gases rush from the cylinder, relieving pressure in the cylinder. The intake ports are opened, and pressurized air fills the cylinder, forcing out the remaining exhaust gases. The exhaust valves close and the piston starts traveling back upward, the intake ports are closed and the fresh charge of air is compressed in the cylinder, in preparation for fuel injection. Four stroke designs also are known.
Engine emission standards have led to the investigation of engine operating and compression ignition alternatives. In one such alternative, referred to as homogenous charge compression ignition (HCCI), significant emission reductions have been experienced during initially testing. In an engine operating under HCCI concepts, the air and fuel are intimately mixed, typically at a high air/fuel ratio, before maximum compression in the combustion cylinder. As a result, each droplet of fuel is surrounded by an excess of combustion air. As compression occurs, the air temperature increases, and ultimately combustion is initiated at numerous locations throughout the cylinder. Typically, combustion commences at lower temperatures than for direct charge ignition, leading to reduced NOx emissions.
The use of homogenous charge compression ignition concepts have apparent benefits in substantial reduction of NOx emissions. However, two aspects of combustion control used regularly in more conventional engines are not available in an HCCI engine. The timing of ignition in an HCCI engine can be controlled neither indirectly by controlling the start of fuel injection as in a direct injection engine, nor directly by controlling spark initiation as in a spark ignition engine. Further, the rate of heat release can not be controlled via control of fuel injection, as in a direct injection engine, nor by flame propagation, as in a spark ignition engine. As a result, ongoing efforts for improving the HCCI concept include ways to control the ignition event in an HCCI engine. Incorporating the HCCI concept in multi-cylinder engine framework presents additional challenges in starting the engine. Further challenges to development of HCCI engine concepts include the incorporation of turbochargers.
Multi-fuel, hybrid engines are known. U.S. Pat. No. 5,010,852 discloses an engine operable in both two stroke and multistroke working cycles.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an internal combustion engine is provided with a plurality of combustion cylinders operable under homogenous charge compression ignition concepts, and at least one combustion cylinder operable on one of spark ignition concepts and direct injection ignition concepts.
In another aspect of the invention, a work machine is provided with an engine including a plurality of combustion cylinders operable under homogenous charger compression ignition concepts; and at least one combustion cylinder operable under one of spark ignition concepts and direct injection ignition concepts.
In a further aspect of the invention, a method for operating an internal combustion engine is provided with steps of providing a plurality of combustion cylinders; operating the plurality of combustion cylinders under homogenous charge compression ignition concepts; providing at least one further combustion cylinder; and operating the at least one further cylinder under spark ignition concepts.